An evaporator leak is one of the most expensive AC repairs because the evaporator sits inside the dash. Signs include cooling that fades over a season, no visible leak under the hood, and a sweet smell from the vents.
Aluminum evaporators corrode from condensation over many years. A pinhole develops and refrigerant slowly escapes into the HVAC duct. Cooling fades by season and no leak shows under the hood.
The brazed joints where lines connect to the evaporator can crack from vibration. Same symptoms as pinhole but sometimes detectable with a sniffer at the vent.
Less common than core failure but cheaper to fix. The O-rings where evaporator tubes pass through the firewall can dry out and leak.
Mixing R134a and R1234yf or using off-spec refrigerant creates acids that eat the evaporator. Less common but devastating when it happens.
A stuck-shut expansion valve sends extreme pressure to the evaporator, eventually cracking it. Original failure was the TXV but the result is an evaporator repair.
Over-torqued fittings during a previous repair can crack the aluminum. Sometimes shows up months after the work.
A blower motor that shed metal debris can puncture the evaporator from the airflow side. Rare but possible.
| Likely Cause | Typical Cost | DIY Difficulty | Severity | Likelihood |
|---|---|---|---|---|
| Pinhole Corrosion in Evaporator Core | $800-$1,500 + 4-8 hrs | Hard | High | 70% |
| Cracked Evaporator Fitting | $800-$1,500 + 4-8 hrs | Hard | High | 40% |
| O-Ring at Evaporator Inlet | $50-$150 O-rings + 2-3 hrs | Hard | Medium | 25% |
| Acid Attack From Mixed Refrigerants | $1,000-$2,500 full system flush | Hard | High | 15% |
| TXV Failure Causing Evaporator Pressure Spike | $1,000-$1,800 evap + TXV + drier | Hard | High | 10% |
| Stress Crack From Improper Service | $800-$1,500 + 4-8 hrs | Hard | High | 8% |
| Foreign Object Damage | $800-$1,500 + 4-8 hrs | Hard | High | 5% |
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Cooling fades over weeks. No visible leak under the hood. UV dye on the evaporator drain after running AC for several days. A shop with a sniffer can detect refrigerant at the cabin vents.
$800-$1,500 on most cars. Some require dash removal which can push it to $2,000+. Get a written estimate before authorizing.
Short term yes but venting refrigerant is illegal and you are throwing money away. Each recharge costs $150-$250 and the system fails again within months.
Compare to vehicle value. On a $5,000 car, a $1,500 evaporator is borderline. On a $20,000 car, it is worth it.
10-15 years on most cars. Some last the life of the car. Some fail at 8 years.
Yes. Any time the system is opened to atmosphere for a major repair, replace the drier (mandatory) and consider the expansion valve (recommended) while the system is apart.
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